Do you wake up each morning on your own without an alarm clock feeling refreshed, alert and ready for the day ahead? Or do you drag yourself out of bed, grumbling to yourself until you get your first cup of coffee?
Most Americans, unfortunately, fall into the latter category. And the situation is getting worse. Between surveys taken in 1959 and 1992, middle aged adults reported that their average sleep duration decreased by about an hour–to 7-8 hours of sleep a night. Another study based on sleep records of full-time workers found a significant increase in the number of persons getting less than six hours of sleep a night during the period from 1975 to 2006.
Most of us yearn for more sleep than we’re able to get, particularly when we’re in college or have small children. Sleep becomes a habit, and, with the help of a few cups of coffee, we usually get by on whatever snooze time we’re able to get and may not even feel deprived.
Studies indicate, however, that sleep plays an important role in good health and even longevity. Persons who average 6.5 to 7.5 hours of sleep a night (according to self reports) live longer than those who sleep less and even those who sleep more.
The effect of short sleep is easy to understand. Even over a one- to two-day period, subjects limited to four hours of sleep show increased heart rate and blood pressure and markers of inflammation such as c-reactive protein (CRP)–all risk factors for heart disease. This kind of sleep deprivation is also associated with impaired glucose tolerance, leading to increased hunger/appetite, obesity and type 2 diabetes.
Surveys of large numbers of American adults have shown a correlation over the long term between restricted sleep and hypertension, diabetes, weight gain and reduced immune function.
Up to this point, studies have not found similar negative physical changes associated with long sleep duration, although observational studies indicate that long sleepers have an increased risk of illness, accidents, depression and death.
Some researchers believe that the body will not allow us to over-sleep and that many persons who habitually sleep 9 or 10 hours a night might have depression or a physical illness that accounts for their longer sleeping and greater risk of early death.
How Much Do We Need?
Although they have been studying sleep intensely over the past several decades, scientists have yet to discover exactly why sleep is so important, what it does for our minds and bodies. And there remains the question: how much sleep do we really need?
Age is a major factor. Newborns spend about 16 hours every day in sleep, and sleep time gradually decreases through age three. Elementary school children generally need 10 to 12 hours of sleep a night while adolescents can get by with 8 to 9 hours.
For adults, most experts agree that there is no magic number and that there is a great deal of individual variation. Some individuals go through most of their lives getting less than five hours sleep a night while others seem to require 9 to 10 or more.
When you were in college and “pulled all nighters” to study for examinations, you probably assumed your mind and body would adjust–that your cramming would help you pass the test and that you could catch up on lost sleep when exam week was over. Studies over the last decade indicate that this was probably not the case.
In a 2003 study, David Dinges and Hans Van Dongen of the University of Pennsylvania assigned subjects to groups sleeping four, six or eight hours for two week periods in the sleep laboratory. Every two hours during the day, the subjects were given a psychomotor vigilance test, measuring the kind of sustained attention and focus that are needed for tasks such as driving, careful reading of an exam question or working a math problem.
Over the study period, subjects getting eight hours of sleep had no lapses of attention or cognitive impairment, but those in both of the other groups showed steady declines with each passing day. By the end of two weeks, those sleeping six hours a night had cognitive impairments similar to subjects in another study deprived of sleep for 24 hours straight.
At first, the sleep deprived subjects realized that they were not at their best, but as time went on, they insisted they had adjusted and that sleepiness was no longer affecting their performance–even though it clearly was.
How about increasing sleep time? One study asked students to “sleep as much as possible” over several weeks. During the first week, the subjects’ average sleep time increased from 7.5 to 9-9.9 hours a night, and these increased sleep times were associated with better alertness and less daytime sleepiness.
Over the next several weeks, however, the students’ sleep time gradually came back down to an average of about 8.5 hours a night. The researchers theorized that the subjects probably made up for previous sleep deprivation, then reached their maximum sleep level during the following weeks.
Researchers continue to study the interaction between 1) basal sleep need and 2) sleep debt. The first refers to the sleep needed on a regular basis–seven to eight hours for most persons. Sleep debt occurs when you fail to meet that basal need because of sickness, stress, poor sleep habits or simply a busy schedule.
A two-hour sleep loss from one night is relatively easy to make up with one or two satisfying sleep sessions. When you lose an hour or more each night over a couple of weeks, however, the debt can become substantial and more likely to cause impairments in thinking, learning, memory or mood. Sleep debts can be paid off, although the process may not be a simple hour for hour re-payment. One or two nights of sleeping in over the weekend is usually not enough to erase the debt and get us back to optimal alertness.
When pressed by a busy schedule, it’s tempting to sacrifice an hour or two of sleep–sometimes on a regular basis–in order to get things done. Unless you’re doing something that requires little thought, that may not be a smart idea. As one researcher put it, you may be “trading time awake at the expense of performance.”
REFERENCES:
Chris Adams, “How much sleep do you need?” About.com Guide.
Joe Barber, Jr., Ph.D., “Insulin sensitivity may be impaired by sleep restriction,” Medscape Medical News, October 16, 2012 (Annals of Internal Medicine, 2012;157:549-557.
Laurie Barclay, M.D., “Alcohol use for sleep strongly linked to hazardous vs moderate drinking,” Medscape Medical News, November 8, 2010 (Annals of Family Medicine, 2010;8:484-492).
Gail Belsky, “How much sleep do you really need?” Health Magazine.
Laura Blue, “How much sleep do you really need?” Time Health, June 6, 2006.
Michael A. Bonnet, Ph.D., “How much sleep do we really need?” National Sleep Foundation.
Michael A. Bonnet, Ph.D., and Donna L. Arand, Ph.D., “How much sleep do adults need?” National Sleep Foundation White Papers.
Deborah Brauser, “Sleep quality now may affect cognition later,” Medscape Medical News, July 16, 2012.
Megan Brooks, “Sleep time and quality vary by race, native country,” Medscape Medical News, June 21, 2012 (Sleep, 2012).
Megan Brooks, “Sleep loss may fuel poor food choices,” Medscape Medical News, June 11, 2012 (Sleep, 2012).
Megan Brooks, “Lack of sleep ups stroke risk in low-risk adults,” Medscape Medical News, June 13, 2012 (Sleep, 2012).
Hans PA Van Dongen, Naomi L. Rogers and David F. Dinges, “Sleep debt: theoretical and empirical issues,” Sleep and Biological Rhythms, 2003;1:5-13.
Emma Hitt, Ph.D., “Sleep duration linked to vaccine response,” Medscape Medical News, August 7, 2012 (Sleep, 2012;35:1063-1069).
“How much sleep do children need?” WebMD Health & Parenting Medical Reference, reviewed by Roy Benaroch, M.D., February 6, 2012.
Maggie Jones, “How little sleep can you get away with?” New York Times April 15, 2011.
Daniel M. Keller, Ph.D., “Sleep quantity and quality predict ability to lose weight,” Medscape Medical News, May 25, 2012.
Nick Mulcahy, “Lack of sleep linked to breast cancer aggressiveness in postmenopausal women only,” Medscape Medical News, September 7, 2012 (Breast Cancer Research and Treatment, 2012;134:1291-1295).
Amy Norton, “Smokers may have more sleep problems,” Reuters Health, September 16, 2012 (Addiction Biology, 2012).
11/29/2012
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